170 Mr. W. K. Fisher on Asteroidea. 
Asteroidea, 1889, p. 192, as the first diagnosis in the ‘* Narra- 
tive of the ‘Challenger’? Expedition” (vol. i. p. 609) con- 
tained no specific names. The first species, and only adult 
form, is L. tartareus, and this may serve as type. The other 
species, L. forcipifer, seems to be founded upon immature, or, 
at least, very small specimens, and whether the adult is like 
tartareus or a species of Dipszcaster is not known. L. tar- 
tareus has a small spine on each marginal plate, rather small 
actinal interradial areas, and seems to me to be near Dytaster. 
I have seen the type in the British Museum. 
Metrodira, Gray,and its Systematic Pusition.—This puzzling 
genus was placed in the Linckiidee by Sladen (* Challenger ’ 
Asteroidea, 1889, p. 415), and other writers have followed 
him. 
Metrodira shows an outward resemblance to the Asteropide, 
harring the single feature of the slender rays. De Loriol * 
described a very young specimen as Scaphaster humberti, 
which he placed in the Gymnasteriida (=Asteropide) near 
Asteropsts (= Petricia, Gray). 
Sladen (loc. cit.) stated that “its external facies and 
general structure appear to indicate an intermediate position 
between the Linckiide and HKchinasteride.” 
Unfortunately the specimens at my disposal are small. 
The characters which would lead one to place this genus in 
the Asteropide (restricted to Astervpe and Petricia) are as 
follows ;—The thin skin which covers the plates and spines ; 
the conspicuous marginals, not unlike those of Petricia; the 
loosely tessellate abactinal skeleton, bearing skin-covered 
spinelets. The characters which are adverse, so to speak, 
are:—The conspicuous series of intermarginal plates, the 
absence of actinal intermediate plates, except a single plate 
back of the moutlh-plates; the rudimentary interbrachial 
septum without.a calcareous pillar (perhaps due to small size 
of disk) ; the single ampulla to each tube-foot. 
The teatures which seem to ally Aletrodira to the Echin- 
asteride are :—The single ampullee, spinose abactinal plates, 
and the adambulacral armature. The intermarginal plates 
and the very reduced actinal intermediate areas are entirely 
consistent with this family, but the very conspicuous mar- 
ginal plates arenot. ‘The interbrachial septa are rudimentary, 
practically absent, although it is not possible in the small 
specimens at my disposal to be certain of this point. 
eres soc. phys. et d’hist. natur. Genéve, vol. xxxiii. pt. 2, no. 1, 
p26 . 
SNe Ve 
